In the inkjet printing technology, ink droplets are printed into pixels by a printing injection head. Using the inkjet printing technology to fabricate OLED display products has advantages such as high material utilization, short fabrication time and the like. Thus, employing the inkjet printing technology to fabricate OLED display products has gained a broad attention, and has become a focus of development. Fabricating OLED display products utilizing the inkjet printing technology requires relatively high accuracy of a printing position and relatively high accuracy of an ink droplet volume. If the accuracy of a printing position is not high enough, then an ink droplet cannot enter a pixel; if the precision of an ink droplet volume is not high enough, then a case of non-uniform display arises. Therefore, for the performance of a fabricated product, it is crucial to precisely measure a volume of an ink droplet.
Existing inkjet printing apparatus typically employs an optical measurement approach to measure a volume of an ink droplet. A single ink droplet can be precisely measured using the optical measurement approach, with a short measurement time. The optical measurement approach forms an optical image of an ink droplet, and then performs a fitting process on the image to calculate a volume of the ink droplet. Thus, the optical measurement approach has a relatively large error.
FIG. 1 is a schematic diagram in which an ink droplet is being measured using the optical measurement approach in the prior art, and FIG. 2 is an enlarged view of part A in FIG. 1.
Referring to FIGS. 1 and 2, a part A is a boundary profile of an ink droplet 104, and a part B is a center position of the ink droplet 104. There are two types of errors produced by the optical measurement approach: one is a type of error caused by a resolving power of an optical lens; and the other is a type of error resulting from an estimation of the center position. Furthermore, there is also a problem of difficulty in finding optimal measurement parameters in the optical measurement approach, which may also lead to a measurement error. In addition, different types of ink droplets have different refractive index for light, which also causes measurement error.